Help - Search - Members - Calendar
Full Version: Geomorphology of Gale Crater
Unmanned Spaceflight.com > Mars & Missions > MSL
Pages: 1, 2, 3, 4, 5, 6
dvandorn
QUOTE (serpens @ Dec 22 2012, 05:00 PM) *
...Iím not sure what effect the model start premise that the crater floor was non-erodible basalt has since it was more likely erosion susceptible breccia/suevite.

That depends on what filled the crater after it was formed. The floor is obviously made of some kind of fill -- Gale at present is nowhere near as deep as it would be if the floor was the original impact-melt-lined bowl.

If water and wind transport caused the entire crater fill, then at the very beginning of the process, you're right, it would be filling directly onto a brecciated floor covered by a relatively thin layer of impact melt. However, if the impact opened up a vent to an active lava conduit, the floor of Gale could have been filled in with a solid basaltic plug before the slower deposition and deflation processes began to carve and rearrange what was left. I get the feeling this is the kind of start point the model you mention is positing.

-the other Doug
serpens
Yeah, that's a possible scenario although I'm not sure that it is a common outcome in a final crater bowl? But my reservation was more on the effect on the model of a single start point (I assume the initial floor type is of some significance else why mention it in such a short article). Based on the apparent clay beds and the nature of the terrain Curiosity is currently investigating the possibility of initial lacustrine/deltaic sediments would seem worth consideration. Or if there was an inner ring, even a start scenario of a water filled moat between crater wall and inner ring, with mound building internal to the inner ring. Intuitively an inner ring would create some interesting interactions with katabatic winds flowing from the circumference towards the centre.
fredk
Sorry if this was discussed already, but there's a story at Science (subscription required, unfortunately) that talks about the history of Gale according to Kevin Lewis and Edwin Kite.
Eyesonmars
Yes. I posted a link to their paper a couple days ago. No paywall. Look back a dozen or so posts
edwinkite
That was our submitted version. The in-press version is here: http://gps.caltech.edu/~kite/doc/Kite_et_al_Gale_Mound.pdf
We made several relatively minor changes in response to a useful review by Ryan Anderson, and also ran some 3D simulations as a sanity check on the assumptions in the 1D model.
Eyesonmars
The fact that the very dark (black) supposedly basaltic sand dunes that partially surround the mound
are completely devoid of red dust has puzzled me. This may help explain it. Assuming the dunes are heavier sand.

Also. The bulk of the mound appears to be shifted north of the crater center. Stronger katabatic winds from the
higher crater rim to the south might explain this. Interestingly the very top of the mound seems to shift back toward the crater center
dvandorn
Very dark to black sand dune structures aren't all that uncommon on Mars. In fact, we've studied one closely -- El Dorado at Gusev.

It would seem that certain Martian wind shadows set up a process that sorts for the grain size of the black sands.

-the other Doug
JRehling
Indeed, and I had the pleasure of riding a bicycle into a dust devil once (with appropriate safeguards: goggles and kerchief).

Also, I learned when I once saw tumbleweeds appear to be juggled by an invisible giant, dust devils are often there without the dust. We only see them when the cyclone has some dust to grab. Which happens to be common in some places.
SFJCody
Weirdly, the only time I've ever actually seen a dust devil here on Earth was when I was standing watching of one of the big DSN antennas at the Madrid DSCC as it was pointed towards Mars. It looked just like the ones that Spirit saw!
serpens
QUOTE (dvandorn @ Dec 25 2012, 01:26 AM) *
It would seem that certain Martian wind shadows set up a process that sorts for the grain size of the black sands.


Yep, aeolian sorting and accumulation based on grain size/density is a feature of sandy deserts on Earth and from what we have observed, on Mars. From observation by Spirit and Opportunity silt surfaces/dunes are armored by a thin veneer of larger sand sized grains (and in the case of Meridiani smaller concretions and fragments). Potentially the size of these armoring grains could provide an indication of the wind velocity at the time that the dunes froze. Since the upper reaches of Mount Sharp are presumably made up of unconsolidated deposits including some dunes, correlation of observed armor grain size to wind speed could be an interesting data point.
iMPREPREX
Do we know what these "mini volcanoes" are and how they came about?

From my Sol 137 mosaic. I annotated a few of them with black arrows.


Gladstoner
.
dvandorn
Yep, these look an awful lot like eroded clasts to me. What fascinates me even more then the bubblies, though, is the overall look of the terrain. I've seen undercut rocks like this many times, in both wet and dry streams here on Earth.

Here is a rather basic question -- the aerial views of this region appear to show alluvial features here. And the ground-based images show what strongly resemble water-cut rock overhangs. However, when we discuss surface rock erosion, it seems like you get Looked At Funny if you speak about the possibility of water erosion, as if suggesting that any close-in surface feature shows any remnant of water erosion just means you don't understand that Mars has been arid for billions of years.

If it looks like water erosion from above and from the surface, don't we have to at least give serious consideration to the possibility that at least some of the terrain we see around us is, in fact, the direct result of flowing water? Perhaps preserved for billions of years, but water-cut nonetheless? Sort of following the logic path of "if it looks like a duck and quacks like a duck, maybe it is a duck."

-the other Doug

p.s. -- I'm visiting family for the holidays, and the only way I really have of following the forum is via my Kindle Fire, and it's a longer process than normal trying to type with the on-screen keyboard, so I won't be posting a huge amount. Great for looking at the pictures, though.
Gerald
I'm trying to get comfortable with the idea, that the supposed liquid may have been sulfuric acid with solved sulfates, and quartz suspension.
Eyesonmars
There are two articles in the most recent issue of Icarus that we all might take a look at that might influence our interpretation of curiosity's current environs. Using the latest spectroscopic parameters for CO2 as well as a detailed cloud microphysics parameterization the authors make the case for an extremely cold ancient Mars in which the periodic collapse of the atmosphere might occur even with up to 7 bars of CO2. Imagine what might happen at the base of a Co2 glacier say 100 meters or greater in thickness if a modest amount of geothermal heating lifts the base temperature to 224K.

Im on a ski trip doing this on my iphone so pardon my brevity and for not posting links
Gerald
The "missing links" to the articles about early Mars climate:
Abstract
Full text

The other article

EDIT: For the Hesperian, I think, one should take into account the acidity of water. Sulfuric acid may decrease the freezing point of water.
serpens
Is the outcome of this a re-run of Nick Hoffman's white mars hypothesis? He made a good hypothetical case, but the physical and geochemical indications garnered by Opportunity over the years present compelling evidence for long lasting liquid groundwater with periodic surface exposure. As far as Curiosity's current environment is concerned I'm in the Other Doug's camp with respect to the fluvial provenance of this area. But keeping an open mind, the cementing agent in the sediment (and what appears to be significant variations in lithification) will provide a good indication of the environment in which it formed.
dburt
QUOTE (serpens @ Dec 28 2012, 03:40 PM) *
...the physical and geochemical indications garnered by Opportunity over the years present compelling evidence for long lasting liquid groundwater with periodic surface exposure. ...

That particular interpretation is still open to debate, and has already been debated extensively here and in various published articles over 5 years ago. Widespread clay minerals, reported in Gale but not Meridiani, presumably provide the best evidence for some type of liquid water or steam. The cementing agents for the weak clastic sediments visited by the first two exploration rovers on Mars appear to be various reactive, soluble salts, including acid salts - not exactly compelling evidence for persistent surface or ground water. I'll leave it at that. Please PM me if you wish clarification or a longer discussion.
- dburt
drz1111
I'm very sceptical of models of what climate "should" have been for early Mars. Similar models completely fail to explain the undisputed evidence for widespread liquid water, and modern-type fluvial erosion, on Hadean earth. There's a bug in our understanding of that time.
serpens
I share your scepticism. Given the track record of climate modellers on Earth where outcomes do not reflect predictions despite the ability to empirically measure input constants and variables, it is difficult to accept at face value the output of models directed billions of years into the past for an alien planet where many of the inputs must, of necessity, be guestimates.
drz1111
It's more than that. Climate models for the contemporary earth are quite good, unless we're talking about regional details not particularly relevant to an analysis of the global Mars climate. Heck, the models seem to do a pretty good job back through the entire Phanerozoic; they even can go beyond that and describe the "Snowball Earth".

But those same models can't handle the Hadean - specifically, the existence of sufficient quantities of liquid water to support modern-type sedimentary processes and/or the generation of felsic crust - based upon best estimates of insolation at that time, without some pretty improbable assumptions. And if they can't describe Earth, it's hard to imagine why they'd get Mars right. We're missing a piece of the puzzle.
Gerald
Pure climate models will be insufficient for a description of early telluric planets, I think. They should be extended e.g. by gravitational shrinkage heat, radioactive decay heat, impact heat, chemical reaction heat like serpentinization to become more appropriate, imho.
Zelenyikot
Somebody has access to the full text? Interestingly about what it.
http://www.sciencemag.org/content/338/6114/1522.1.summary
Eyesonmars
QUOTE (edwinkite @ Dec 24 2012, 08:21 PM) *
That was our submitted version. The in-press version is here: http://gps.caltech.edu/~kite/doc/Kite_et_al_Gale_Mound.pdf
We made several relatively minor changes in response to a useful review by Ryan Anderson, and also ran some 3D simulations as a sanity check on the assumptions in the 1D model.

Are you referring to this?
Explorer1
This is essentially a news article, so I'm wondering why it's behind a paywall. No matter, I have access through my university. In essence: the researchers say that since the mound's sediment layers are inclined 2-4 degrees from the horizontal (according to MRO observations), as well as the fact that none of the eroded beds reaches the crater wall, the mound is not a remnant of a sediment layer (from an old lake, say) that completely filled Gale.
Instead, they say it was primarily aeolian processes building up an enormous pile of dust. Intense winds from solar heating and air movement could have propelled its' creation from essentially nothing. Water may have been involved at some point, but only marginally.

I hope this helps.
Zelenyikot
Yes, thanks, for an explanation.
Gerald
Inclination might be a result of erosion and creeping, or a result of preferred sedimentation near the mound. Indications for clay minerals in the lower layers of Mt. Sharp still have to be explained. High D/H ratio and a high level of chemically bound water (Rocknest soil) indicate a water-rich past (Noachian) of Mars. The conglomerate finding at Curiosity's landing site strongly indicates a water-rich period. A layer in Yellowknife Bay looks much like containing bound water from the Hesperian (to be confirmed). The crater rim probably is younger as Mt. Sharp, this was assumed before. Science is an adventure; I don't feel any damper.
Eyesonmars

And don't forget the fairly extensive "box works". smile.gif
serpens
The clay at the base of the mound has been identified as nontronite, indicating a wet, neutral pH environment when it formed. When Curiosity gets to the trough we should get an idea of how the smectite bearing layer formed but the extensive indications of water inflow from the rim and on the floor make a shallow lake a real possibility. Smectites consume acidity and the rate of mineral dissolution increases as the pH falls, the end product being amorphous silica. So the survival of the smectites indicates that they were protected from acid waters during the sulphate period. From Ryan Anderson and James Bell's analysis, what they term as the light toned ridge material sandwiches the nontronite layer. I guess that if it was a smectite dissolution product that would have been identifiable so it must have been impermeable.

The katabatic / slope winds hypothesis makes a lot of sense, particularly for the upper mound, but the early history seems fluvial.
elakdawalla
One thing I would want to check is the direction of the tilt and how that relates to the long-term changes in Mars' shape due to, say, the construction of the Tharsis volcanic complex. The MESSENGER team has shown how lava-filled craters near Mercury's pole now have tilted floors that must once have been horizontal, due to tectonic activity. My own work on Venus dealt with the same thing, measuring current topography of lava surfaces that you assume started out as flat in order to get at ancient tectonics. I'm sure the same could happen on Mars. We certainly know Mars' shape has changed in the past, and it's been suggested that the entire crust has reoriented (true polar wander). I'd love to see if the tilting observed here is consistent with geophysical work on Mars' tectonics -- or inconsistent, which would be just as interesting.
Eyesonmars
If "true polar wander" did occur in the past that means GALE crater could have been at a higher latitude when some of these fluvial features were created. Are there any constraints on this imposed by the formation of the tharsis bulge ( which wants to be on the equator i assume)? Do we even know if Gale and/or its fluvial geomorphology formed before, during, or after Tharsis?
chuckclark
QUOTE (elakdawalla @ Jan 1 2013, 06:15 PM) *
check the direction of tilt and how that relates to long-term changes in Mars' shape due to, say, the construction of the Tharsis volcanic complex. Mars' shape has changed in the past, and it's been suggested that the entire crust has reoriented (true polar wander). I'd love to see if the tilting observed here is consistent with geophysical work on Mars' tectonics -- or inconsistent, which would be just as interesting.


Sound like a puzzle that might be unscramble-able with constant-scale natural boundary mapping. If the tilting blocks can be identified (say by constructing the medial axis of all the surface that is not the Tharsis complex, and using that topological skeleton to form the edge of the CSNB map (same as, or similar to, the way the foldable asteroid maps were laid out), then we'd have, perhaps (I'm just making this up as I go along), an ideal map in which to contemplate all the data and speculations about tilt.

And then again, the inverse map, the one that uses critical boundaries within Tharsis complex as the CSNB map edge may be better to project the stresses to the antipodes, which would then by in the middle of the Tharsis-edged map. See some tilting scenarios may be seen as more likely than others.

The nice point is that the two topological skeletons would be complementary to each other, so all sorts of analysis by numerical and (with the handy constant-scale critical boundary format) geometrical, i.e., waterlines, (the old Victorian mapmaking treatment of watery shorelines) which would project stresses (and carry second order stresses) onto the other skeleton.
May not even be necessary to have the map, but then a picture's worth, what? I forget the math . . .
serpens
Since Edwin Kite's article generated this discussion it is interesting that he (and others) also wrote a paper on true polar wander a few years ago.

www-eaps.mit.edu/faculty/perron/files/Kite09.pdf
serpens
QUOTE (Eyesonmars @ Jan 2 2013, 01:06 AM) *
If "true polar wander" did occur in the past that means GALE crater could have been at a higher latitude when some of these fluvial features were created.


Based on analysis of tectonic structures,topography and gravity as well as crustal magnetism Zhong Migration of Tharsis volcanism on Mars caused by differential rotation of the lithosphere concludes that that the main Tharis Bulge had migrated to its current location by the end of the Noachian. I think Gale is assessed as being formed in the late Noachian/early Hesperian and if Zhong is correct then Gale has always been equatorial and the tilt in layers would not be attributable to polar wander although I guess that gradual change to the equatorial bulge following the Tharsis realignment could have some influence.

Emily has an impressive ability to generate, with few words, an incentive to research topics that were previously of minor interest.
Gerald
Several of the rocks near the border of Yellowknife Bay look to me like creeping.
Seasonal temperature cycling might lead to a creeping of the top layer in the direction of the net force, if the top layer consists of material sufficiently different from the layer below.
Might it be, that slope winds exert a force to the top-layer rocks strong enough to result in a net movement towards the crater rim?
An annual creeping of 1mm will be sufficient to exceed aeolian abrasion (0.01 to 0.05 mm per year estimated) twenty- to one hundredfold.

A rough sample calculation, assuming one creeping step per (Earth) year, i.e. two per Marsian year, a difference of the linear thermal expansion coefficients of the two layers of 10 ppm per Kelvin, a seasonal temperature difference of 20 Kelvin, and a length of a rock fragment of five meters yields
0.00001/K x 20 K x 5000mm x 0.5 = 0.5 mm
annual creeping. (Factor one half, because I have to look at the center of the rock.)

For small and thin rocks, even diurnal creeping may occur.
JRehling
This may touch only tangentially on the case of Gale, but I was struck recently upon learning that a 100 km lunar crater, Icarus, also has a central peak that is higher than its rim. Because, obviously, the Moon lacks many of the mechanisms that act on Mars, it offers a far narrower set of possible explanations. In fact, I'm not sure if anyone has explained the case of Icarus. I see a citation of one article I can't read without disbursing some cash:

http://www.sciencedirect.com/science/artic...019103573900237

That said, it is certain that Mt. Sharp has undergone a lot of phenomena that could not be shared between the two cases, but it's interesting to note the lunar case when trying to piece together the logic of Mt. Sharp.
Phil Stooke
Save your cash! There's nothing in that paper about the crater Icarus - it was published in the journal Icarus! (is that where a search led you astray?) There is also absolutely nothing in that paper about any central peak higher than the rim of its crater. LOLA data will allow this topic to be explored much better than any past studies have done.

Phil

elakdawalla
Sorry, Gerald, what you're describing makes no physical sense, and multiplying a couple of numbers together doesn't make it any more sensible. I encourage you to read a physical geology textbook and then ideally a geophysics textbook -- or take some classes -- before trying to do quantitative geophysics. I like both Press & Siever (Earth) and Monroe & Wicander (Physical Geology) as introductory texts, though my textbooks are aging now and there may be better ones out there.

As Phil has said before this forum is better at image processing than geology.
JRehling
Thanks for the tip, Phil. Actually, it was not an errant search, but a comment online by the author of the article who cited it in reference to that crater, but the relevance he inferred to the case of the crater Icarus may have been largely (or entirely) overstated. There may be no scholarly work at all on the case of the lunar crater Icarus.
Gerald
Thanks Emily, for the hints to appropriate literature! It's difficult to find literature, that is not based on conditions observed on Earth.

I looked for investigations of soil creeping on Earth in the web, before I wrote the post. Unfortunately on Earth there is almost always water involved, which leads to additional expansion and shrinking by binding and releasing water to rock containing clay minerals, so that those processes may lead to an estimated soil creeping of about 1cm per year, less than solifluction, so it is mostly negligible on Earth. This may not be obvious for Mars. Therefore I redid the calculations based purely on temperature cycling. Normally such creeping occurs on slightly inclined layers or even within a layer. So the creeping will per se be a valid physical process. The question to me is, whether the thin atmosphere of Mars can exert a net force.

If the creeping as a valid process looks questionable, I may describe the mechanics behind that. In literature it is mostly sketched very briefly, because it's rather easy.

The idea of soil creeping on Mars is not quite new, see Paper on soil ceeping on Mars

drz1111
QUOTE (elakdawalla @ Jan 10 2013, 01:54 PM) *
Sorry, Gerald, what you're describing makes no physical sense, and multiplying a couple of numbers together doesn't make it any more sensible. I encourage you to read a physical geology textbook and then ideally a geophysics textbook -- or take some classes -- before trying to do quantitative geophysics. I like both Press & Siever (Earth) and Monroe & Wicander (Physical Geology) as introductory texts, though my textbooks are aging now and there may be better ones out there.

As Phil has said before this forum is better at image processing than geology.



QFT. Sigh.
Gerald
Thanks JRehling, thanks Phil, thanks Emily, thanks drz1111 for your assessments, and for being honest!
The idea is either too brilliant, or nonsensical, probably the second.
I'll return to image processing.

EDIT: Luckily, I came across the literature, where I originally found an explanation of soil creeping, including quantitative estimates:
David John Briggs, Peter Smithson: "Fundamentals of Physical Geography", p. 325.
Just in case, someone is interested.
ngunn
Speculating about processes on other planets is a better way to spend your time than many others. I do it a lot and in the case of Mars I know I'm 'getting warm' when one or more of the real geologists here responds. There have on many occasions been good geological discussions on this forum even if it isn't what we're best at.

On another tack: crowd sourcing is becoming fashionable in science, mainly for searching through large data sets. I think it can apply also to ideas if similar filtering processes are employed. This forum is perhaps a precursor for what could be done more generally. In the meantime the admins have to keep judging their interventions. It's hard work done for free and I respect them greatly for it.
SFJCody
QUOTE (ngunn @ Jan 11 2013, 09:18 AM) *
Speculating about processes on other planets is a better way to spend your time than many others. I do it a lot and in the case of Mars I know I'm 'getting warm' when one or more of the real geologists here responds. There have on many occasions been good geological discussions on this forum even if it isn't what we're best at.


I'm with ngunn. I enjoy sticking my oar into areas I have no strong specialist knowledge of (hey, it's a fun mission, sometimes one can get a little over-excited!) but I'm even happier to be corrected by the better read among us.
TheAnt
QUOTE (Gerald @ Jan 10 2013, 09:32 PM) *
The idea of soil creeping on Mars is not quite new, see Paper on soil ceeping on Mars


A good find there, and you're right it takes humidity in the soil for creeping, in the lower arctic forests the trunks of birch trees get a funny bent shape in such areas. With the temperature as low as they are, and frozen in subsurface layers I thought creeping would not occur, I am all happy again to be proven wrong. =)
ngunn
My favourite LPSC abstract (so far, I'm still reading) : http://www.google.co.uk/url?sa=t&rct=j...d2k&cad=rja
jmknapp
In lieu of movement towards Mt. Sharp, here's an attempt at what a scene might look like from an aerial view when the rover gets there (anaglyph):

Click to view attachment

That's reprojected from a HiRISE image, using the digital terrain model on the HiRISE site. The location is in the large outflow channel that Curiosity may go up to get to the "non-conformity" boundary (at the upper left half of the image), looking kinda like lava flows.
Fran Ontanaya
Can this inconclusive blue green spotty pattern on CRISM where Curiosity has found carbonates be extrapolated to what is seen higher on Mount Sharp, past the blue and magenta sulfates (as seen here: http://www.planetary.org/multimedia/space-...le-crater.html)? It would be something if under the dust it was all phylosillicates, except for a sulfates apron.
serpens
Suffering from a mild case of cabin fever from being stuck inside due to dreadful weather I thought I would resurrect this thread to throw out a few ideas on the dating of Gale. pdf attachment for brevity of post.
Gerald
Re 3: Reliably tracking back the orbits of the planets of our solar system more than about 0.5 billion years isn't currently feasible, afaik. Adding the excentricity of Mars' orbit, I don't see convincing evidence for the implicite assumption, that the Martian orbit has been 3.7 billion years ago where it is today.
So, I'd think that there is sufficient space to play with resonances and close encounters with other planets, which may or may not still be present in our solar system. Some planets/planetesimals might have been ejected from the solar system, swallowed by the Sun or the gas giants, or fused to today's planets.
Over long time scales close encounters with other stars might have disturbed the orbits of our planets, too.
The faint sun hypothesis is a hypothesis, and despite theoretical evidence, data are lacking. The activity of stars can vary.
And radiogenic heat has generally been considerably higher in the young solar system than today; so we get the Martian interior as a source of heat.
There is of course still quite some uncertainty about the composition and density of the early Martian atmosphere, as well as of its albedo.
Hence I agree, that an early warm Mars is a mystery, but not because there is a lack of possible solutions, but because there are too many solutions.

Therefore I'd take it as valid to assume surface temperatures as inferred from geology, no matter for which particular physical reason.
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.
Invision Power Board © 2001-2020 Invision Power Services, Inc.